单选题如图所示，用力法且采用图（b）所示的基本体系计算图（a）所示梁，Δ1P为（　　）。<br/> <br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/8325590_0.jpg"><br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/8325590_0_1.png">